Suture anchor with improved drive head

ABSTRACT

A suture anchor is provided including an elongate shank defining a longitudinal axis and having at least one bone-engaging thread formed thereon, and a drive head having a proximal end and a distal end mated to the elongate shank. The drive head has a substantially oval shape and includes at least one suture attachment member formed in a portion of the drive head. The configuration of the drive head is particularly advantages in that it provides a suture anchor having improved physical properties, including a high failure torque and a high stripping strength.

FIELD OF THE INVENTION

The present invention relates to suture anchors having improved physicalproperties, and in particular to suture anchors having a high failuretorque.

BACKGROUND OF THE INVENTION

Suture anchors are often used to attach a length of suture to bone inorder to use the suture to secure detached soft tissue to the bone.Suture anchors typically have an anchor body, a suture attachmentfeature, and a bone engaging feature for retaining the suture anchorwithin bone. The anchor can be inserted into a preformed hole in thebone, and/or the anchor can be self-tapping and thus can include threadsfor mating the anchor within bone. Most suture anchors require the useof an insertion tool for driving the suture anchor into bone. Suchinsertion tools are typically formed from an elongate shank having amating feature formed on a distal end thereof for mating with acorresponding mating feature formed on or in the head of a sutureanchor. One common type of driver tool includes a hex-shaped orsquare-shaped socket for receiving a corresponding hex-shaped orsquare-shaped head of a suture anchor.

While conventional suture anchors and suture anchor drivers aresufficient, they have some drawbacks. Hex-shaped and square-shapedanchor heads, for example, tend to have a relatively low strippingstrength. This can be due to the structural integrity of the anchorhead, which is sometimes weakened by the attachment feature used toattach a suture to the anchor head. If the attachment feature decreasesthe amount of material on the anchor head that interfaces with thedriver, then the amount of material that needs to be removed or“stripped” from the drive head is reduced, thus reducing the strippingstrength of the head.

Conventional suture anchor heads also tend to have a relatively lowfailure torque, which can result in shearing of the head duringinsertion. This type of failure can also be caused by the location ofthe suture attachment feature on the anchor head, which can reduce theoverall cross-sectional area of the drive head. The Bio-corkscrew™anchor, manufactured by Arthrex Inc., of Naples, Fla., is one example ofa suture anchor having a suture attachment feature that can interferewith the structural integrity of the anchor. In particular, a loop ismolded into and embedded within the anchor such that the loop extendsoutward from the head of the anchor to receive a suture. As a result ofthe placement of the looped suture through the anchor, the entire anchorhead is relatively weak and thus has the potential to shear off duringinsertion.

One option to increase the failure torque of an anchor head is toincrease the size of the head. Large anchor heads, however, require alarge driver tool, which in turn requires a relatively large bone tunnelto be formed in the bone. This is particularly undesirable, especiallywhere the bone tunnel is to be formed in the cancellous bone.Accordingly, most suture anchors are adapted to for use with arelatively small driver tool, and thus they have a relatively smalldrive head which can result in a low failure torque and a low strippingstrength.

Accordingly, there remains a need for suture anchors having improvedphysical properties, and in particular having a high failure torque anda high stripping strength.

SUMMARY OF THE INVENTION

The present invention generally provides a suture anchor including anelongate shank defining a longitudinal axis and having at least onebone-engaging thread formed thereon, and a drive head having a proximalend and a distal end mated to the elongate shank. The drive head has asubstantially oval shape and at least one suture attachment memberformed in a portion of the drive head. The configuration of the drivehead is particularly advantageous in that it provides a suture anchorhaving improved physical properties, including a high failure torque anda high stripping strength. In an exemplary embodiment, the drive headhas a failure torque of at least about 5.0 inch pounds, and the drivehead has a tensile strength of at least about 60 pounds force (lbf).

In one embodiment, the suture attachment member comprises at least onesuture tunnel extending through the drive head, either substantiallytransversely or such that the suture tunnel(s) intersects thelongitudinal axis of the suture anchor. The suture attachment member canalso include a longitudinally oriented suture-receiving channel formedon an outer surface of the drive head and originating at and extendingproximally from each opening of the at least one suture tunnel. In anexemplary embodiment, the suture tunnel(s) are formed proximal to thedistal end of the drive head to present a channel-free portion in thedrive head. The channel-free portion provides additional structuralintegrity to the drive head of the suture anchor to minimize the risk ofshearing during insertion. In another exemplary embodiment, the drivehead includes a first suture tunnel having a first pair of opposedsuture-receiving channels extending proximally therefrom, and a secondsuture tunnel having a second pair of opposed suture-receiving channelsextending proximally therefrom.

In other aspects, a suture anchor and installation kit is providedincluding at least one suture anchor and a cylindrical driver tool. Thesuture anchor has a shank with bone-engaging threads formed thereon anddefining a longitudinal axis. A drive head is formed on the shank andhas an oval shape with at least one longitudinally orientedsuture-receiving channel formed therein. The cylindrical driver tool hasa distal end with a socket formed therein having an oval shape adaptedto receive and engage the drive head of the suture anchor. In anexemplary embodiment, the driver tool has an outer diameter that isequal to or less than an outer-most diameter of the suture anchor.

Methods for using a suture anchor in accordance with the presentinvention are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A is a perspective view of a suture anchor according to oneembodiment of the present invention;

FIG. 1B is another perspective view of the suture anchor shown in FIG.1A;

FIG. 1C is an enlarged, perspective view of the drive head portion ofthe suture anchor shown in FIG. 1A;

FIG. 1D is top view of the suture anchor shown in FIG. 1A;

FIG. 1E is a cross-sectional view of the suture anchor shown in FIG. 1A;

FIG. 1F is a cross-section view of the suture anchor shown in FIG. 1A;

FIG. 2A is a side view of one embodiment of the driver tool inaccordance with the present invention;

FIG. 2B is an end view of the distal-most end of the driver tool shownin FIG. 2A;

FIG. 3A is a top view illustration of the drive head of a suture anchorin accordance with the present invention compared to two prior artsuture anchor drive heads;

FIG. 3B is a top view illustration of the suture anchor drive headsshown in FIG. 3A having shaded areas illustrating the portion of thedrive head that needs to be removed in order to strip the drive head;

FIG. 4 is a chart illustrating the pullout tensile strength of severaldifferent suture anchors compared to a suture anchor in accordance withthe present invention; and

FIG. 5 is a chart illustrating the failure torque of several differentsuture anchors compared to a suture anchor in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1A and 1B, the present invention generally provides asuture anchor 10 including an elongate shank 12 defining a longitudinalaxis A and having at least one bone-engaging thread 14 formed thereon,and a drive head 16 having a proximal end 16 a and a distal end 16 bmated to the elongate shank 12. The drive head 16 has a substantiallyoval shape and includes at least one suture attachment member formedtherein. The configuration of the drive head 16 is particularlyadvantages in that it provides a suture anchor 10 having improvedphysical properties, including a high failure torque and a highstripping strength.

The elongate shank 12 of the suture anchor 10 can have a variety ofconfigurations, and can include a variety of different bone-engagingfeatures formed thereon. FIGS. 1A and 1B illustrate an exemplaryembodiment of a bone anchor 10 having a shank 12 including a core 20with a single helical thread 14 extending around the core 20 from aproximal end 12 a to a distal end 12 b of the shank 12. The thread 14includes proximal and distal facing flanks 14 a, 14 b that extendbetween a root 14 c and a substantially flattened crest 14 d. The thread14 defines a major diameter d₂ of the shank 12, which can vary along thelength of the shank 12, but the major diameter d₂ is preferablysubstantially constant along a substantial portion of the shank 12. Thethreads 14, however, can taper at the distal portion of the shank 12 toterminate at an apex 22 which forms the distal tip of the shank 12. Thecore 20 of the shank 12 defines a minor diameter d₁ that can also besubstantially constant or can vary along the length of the shank 12. Asshown in FIG. 1A, the core 20 tapers from a proximal end 12 a to adistal end 12 b. A person skilled in the art will appreciate that theshank 12 shown in FIG. 1A is merely an exemplary embodiment of a shank12, and that a variety of different shanks having differentbone-engaging features can be used with a suture anchor 10 in accordancewith the present invention.

The head 16 of the suture anchor 10 is shown in more detail in FIGS. 1Cand 1D, and is attached to, or more preferably is formed integrallywith, the shank 12. The head 16 has a generally oval shape defining aminor diameter x₁ and a major diameter x₂. In an exemplary embodiment,the minor diameter x₁ of the head 16 is about three-fourths (¾) the sizeof the major diameter x₂ of the head, and the major diameter x₂ of thehead 16 is equal to or less than the minor diameter d₁ of the shank 12.The relatively small size of the major diameter x₂ of the head 16 ascompared to the minor diameter d₁ of the shank 12 is particularlydesirable so that the head 16 will not require a larger bone tunnel tobe formed in the bone than is necessary. The head 16 further includes alength L_(h) (shown in FIG. 1B) that extends between the proximal anddistal ends 16 a, 16 b thereof. The length L_(h) of the head 16 canvary, but preferably the length L_(h) of the head 16 is optimized toallow the head to be received within a driver tool and to be driven intobone without shearing off.

The head 16 of the suture anchor 10 further includes at least one sutureattachment member formed thereon or therein for receiving one or moresutures. While a variety of suture attachment members can be used, FIGS.1A–1F illustrate an exemplary embodiment of the suture anchor 10 havingfirst and second suture tunnels 26, 27 that extend through the head andthat allow a length of suture to be disposed therethrough. The first andsecond suture tunnels 26, 27 can extend at virtually any orientationthough the anchor head, but as shown in FIGS. 1A, 1E and 1F theypreferably extend transversely through the anchor head 16 at differentpositions along the longitudinal axis A of the anchor 10 to prevent thetunnels from intersecting, so as to preserve the structural integrity ofthe head 16. In an exemplary embodiment, the suture tunnels terminate ata position proximal to the distal end 16 b of the drive head 16 toprovide a channel-free portion 24 (shown in FIG. 1B) in the head 16.Since the distal portion of the anchor head 16 is typically the part ofthe anchor 10 that is under the most stress during insertion, thechannel-free portion 24 provides a much stronger, more dense portion ofthe anchor head 16 that will minimize the risk of shearing duringinsertion.

The suture anchor 10 can also optionally include four longitudinallyoriented suture-receiving grooves or channels 18 a, 18 b, 18 c, 18 dformed therein. The suture-receiving channels 18 a, 18 b, 18 c, 18 d areformed in the outer surface of the head 16 and are preferably spacedequidistant from one another. As shown in FIG. 1D, two opposedsuture-receiving channels 18 d, 18 b are positioned along the majordiameter x₂ of the anchor head 16, and the other two opposedsuture-receiving channels 18 a, 18c are positioned along the minordiameter x₂ of the head 16. The position of the suture-receivingchannels 18 a, 18 b, 18 c, 18 d can also vary, but preferably theyextend through the proximal surface 16 c of the drive head 16 andterminate at an opening of the corresponding suture tunnel. Where thesuture tunnels are positioned proximal to the distal end 16 b of thedrive head 16, the suture-receiving channels 18 a, 18 b, 18 c, 18 dpreferably also terminate at a position proximal to the distal end 16 bof the drive head 16 to provide a channel-free portion 24 (shown in FIG.1B) in the head 16. Moreover, where two suture tunnels are provided atdifferent locations along the length of the drive head 16, a first pairof opposed suture-receiving channels, e.g., suture-receiving channels 18a, 18 b, can have a length L₁ that is different than a length L₂ of asecond pair of opposed suture-receiving channels, e.g., suture-receivingchannels 18 c, 18 d, as shown in FIG. 1C.

The size and depth of each suture-receiving channel 18 a, 18 b, 18 c, 18d can also vary, but they should be effective to seat a suture flush orsub-flush with the head 16 to allow the head 16 to be engaged by adriver tool without interference by the suture. In an exemplaryembodiment, about 20% to 30%, and more preferably about 28%, of across-sectional surface area of the drive-head 16 is removed to form thesuture-receiving channels 18 a, 18 b, 18 c, 18 d. As a result, the drivehead 16, having suture-receiving channels 18 a, 18 b, 18 c, 18 d formedtherein, will have a cross-sectional surface area at the proximal-mostsurface that represents about 72% of a nominal cross-sectional surfacearea within a perimeter of the drive head 16.

A person skilled in the art will appreciate that a variety of techniquescan be used to attach a suture to an anchor, and that the anchor 10 isnot limited to having one or more suture receiving tunnels and/or one ormore suture-receiving channels.

In use, the suture anchor 10 can be driven into bone using a drivertool, such as tool 50 shown in FIG. 2A. The driver tool 50 can have avariety of shapes and sizes, but preferably includes an elongate shaft52 having a proximal, handle portion 54 and a distal end 56 having asocket 58 (FIG. 2B) formed therein and adapted to seat the head 16 ofthe suture anchor 10. The socket 58 of the driver tool 50, which isshown in FIG. 2B, has a substantially oval shape to fit around theoval-shaped head 16 of the anchor 10. The size of the socket 58 shouldbe sufficient to provide a secure fit between the oval-shaped head 16 ofthe anchor 10 and the tool 50, and to prevent rotation of the tool 50with respect to the anchor 10. The driver tool 50 also preferablyincludes an inner lumen (not shown) extending therethrough for receivingthe remaining free ends of the suture(s) threaded through the head 16 ofthe anchor 10.

The suture anchor 10 can be used for a variety of medical procedures. Inan exemplary embodiment, the suture anchor 10 is used in context of anarthroscopic shoulder repair, and more specifically, for attaching adetached labrum (as might result from a Bankart lesion or rotator cufftear) to the glenoid rim of a scapula. It will be understood, however,that the system and method described herein are equally applicable toconnecting detached tissue in other contexts as well. Further, themethod described is merely exemplary of the steps involved in using anyof the embodiments of the anchors of the present invention.

The procedure generally requires a delivery guide, e.g., a hollow guidetube, to be positioned at a desired implant site in the vicinity of ajoint. A tap, or more preferably, an awl or a punch is then insertedthrough the tube and rotated until the depth mark reaches the corticalsurface of the patient's bone. A length of suture is then threadedthrough each tunnel (only tunnel 26 is shown) in the head 16 of theanchor 10, and the remaining portion of the sutures are passed throughthe lumen in the driver tool. The free ends of the sutures extending outof the proximal end 54 of the driver tool 50 can optionally be pulled tohold the suture anchor 10 in the socket 58 of the driver tool 50. Theanchor 10 can be then be inserted into bone by removing the tap from thedelivery guide and introducing the drive tool with the anchor attachedthereto through the delivery guide. The driver tool 50 is then twistedclockwise, applying a slight forward pressure, until the anchor 10 is atthe desired depth. The driver tool 50 can then be removed by pullingstraight back, which will expose the suture anchor and the suturesextending therefrom. The surgeon can then approximate the free end ofdetached labrum to the surface of the bone adjacent to the sutureanchor, and the sutures can then be threaded through detached labrum andtied to secure the detached labrum to the bone.

FIGS. 3A and 3B illustrate the advantages of a suture anchor 10according to the present invention compared to conventional, prior artsuture anchor drive heads, such as the hexagonal-shaped head 70 and thesquare-shaped head 80 shown. Each anchor head 16, 70, 80 shown has asize that is adapted to fit within a driver tool having a socket havingthe same shape as the shape of the corresponding anchor head of theanchor to be driven into bone by the driver tool. The outside diameterof each corresponding driver tool however, is the same for all threeanchor heads 16, 70, 80. During insertion of the anchor into bone, atorque is created by the driver tool 50. At some point, the torquecreated by the driver tool can cause the anchor head to strip, whereinportions of the outer surface of the head are removed thus allowing thehead to rotate within the driver tool. FIG. 3B illustrates the portions72, 42, 82 that would need to be removed in order for each of theillustrated anchor heads 70, 16, 80 to be stripped, e.g., to allowrotation of the anchor head within the socket in the driver tool. Thisis further indicative of the amount of material on the anchor head thatinterfaces with the driver. As shown, the portion 72 of thehexagonal-shaped anchor head that needs to be removed is less than theportion 42 of the anchor head 16 of the present invention that needs tobe removed in order for the anchors to be stripped. The portion 82 ofthe square-shaped anchor head 80 that needs to be removed is moresimilar to the portion 42 on anchor head 16 that needs to be removed toresult in stripping. However, the total cross-sectional area of the ovalanchor head 16 is larger than the total cross-sectional area for thesquare head 80. As a result, the amount of material that interfaces withthe driver on the oval head 16 is much larger than that for the squarehead 80. Thus, overall, the oval head has an increased strippingstrength compared to the prior art anchor heads 70, 80.

The following table, which is based on each of the anchor heads 16, 70,80 having dimensions such that each anchor head 16, 70, 80 is adapted tofit within a driver tool having the same outer diameter, furtherillustrates the differences between the prior art anchor heads 70, 80,and the anchor head 16 of the present invention:

TABLE 1 PERCENT OF MATERIAL THAT TOTAL CROSS- AREA OF MATERIAL THATNEEDS TO BE SECTIONAL SURFACE NEEDS TO BE REMOVED TO REMOVED TO RESULTAnchor Head AREA RESULT IN STRIPPING IN STRIPPING Hexagonal Anchor Head70 0.0089 in² 0.00073 in²  8.2% Oval Anchor Head 16 0.0105 in² 0.00240in² 22.8% Square Anchor Head 80 0.0060 in² 0.00200 in² 33.3%

As shown in Table 1, since the anchor head 16 of the present inventionrequires more material to be removed to result in stripping of the headthan the hexagonal anchor head 70, and since the anchor head 16 of thepresent invention has a much larger cross-sectional surface areacompared to the square anchor head 80, the suture anchor 10 of thepresent invention will have a much higher stripping strength than theprior art anchors. In other words, the anchor head 16 of the presentinvention has a higher driver-to-anchor interface than the prior artanchors.

FIGS. 4 and 5 illustrate further advantages of the anchor 10 of thepresent invention over prior art anchors. The prior art anchors testedinclude the Prior Art 1: 5 mm Hex, the Prior Art 1: 6.5 mm Hex, and thePrior Art 2: 6.5 mm Hex. The Prior Art 1 anchor has a loop molded intoand embedded within the anchor head to receive a length of suture, andthe Prior Art 2 anchor has transverse suture-receiving bores formedtherein. The suture anchors of the present invention are referred to asthe Present Invention: 5 mm Oval, and the Present Invention: 6.5 mmOval. As shown in FIGS. 4 and 5, the anchors of the present inventionhave a pullout tensile, tested using 25D foam, and a failure torque thatis greater than the pullout tensile and failure torque of the prior artanchors. Accordingly, the suture anchor 10 of the present inventionshows a significant improvement over prior art anchors.

The suture anchor 10 of the present invention can be formed from avariety of materials, and can be formed from separate parts which aremated to one another. Preferably, however, the suture anchor 10 isformed as a single unit from a material that is suitable for humanimplantation, such as metal or plastic, and that is somewhat resilient.Exemplary materials include, for example, metals, metal alloys,absorbable polymers, such as, but not limited to, polylactic acid,polyglycolic acid, and copolymers thereof, non-absorbable polymers, suchas, but not limited to, polyethylene, polypropylene, polyurethane, andacetal, and bioceramic materials, such as blends of polymers containingtricalcium phosphate, calcium sulfate, calcium carbonates, and hydroxyappatite.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

1. A suture anchor, comprising: an elongate shank defining alongitudinal axis and having at least one bone-engaging thread formedthereon; and a drive head having a proximal end and a distal end matedto the elongate shank, the drive head having an oval shapedcross-section, at least one suture attachment member, and at least onelongitudinally oriented suture receiving channel formed in a portion ofthe drive head such that a longest dimension of the suture receivingchannel extends parallel to the longitudinal axis of the elongate shank.2. The suture anchor of claim 1, wherein the suture attachment membercomprises at least one suture tunnel extending transversely through thedrive head.
 3. The suture anchor of claim 2, wherein the at least onelongitudinally oriented suture receiving channel is formed in an outersurface of the drive head and originates at and extends proximally fromeach opening of the at least one suture tunnel.
 4. The suture anchor ofclaim 3, wherein the at least one suture tunnel is formed proximal tothe distal end of the drive head to form a channel-free portion in thedrive head.
 5. The suture anchor of claim 3, wherein thesuture-receiving channels are adapted to seat a suture flush orsub-flush with the outer surface of the drive head.
 6. The suture anchorof claim 1, wherein the suture attachment member comprises a first,transversely oriented suture tunnel extending between a first pair ofopposed, longitudinally oriented suture-receiving channels formed in anouter surface of the drive head, and a second transversely orientedsuture tunnel extending between a second pair of opposed, longitudinallyoriented suture-receiving channels formed in an outer surface of thedrive head.
 7. The suture anchor of claim 6, wherein thesuture-receiving channels are adapted to seat a suture flush orsub-flush with the outer surface of the drive head.
 8. The suture anchorof claim 6, wherein the drive head has a cross-sectional surface area atthe proximal-most surface that represents about 72% of a nominalcross-sectional surface area within a perimeter of the drive head. 9.The suture anchor of claim 6, wherein the first and second suturetunnels are formed proximal to the distal end of the drive head to forma channel-free portion in the drive head.
 10. The suture anchor of claim1, wherein the drive head has a failure torque of at least about 5.0inch pounds.
 11. The suture anchor of claim 1, wherein the at least onebone-engaging thread comprises a helical thread.
 12. The suture anchorof claim 1, wherein the elongate shank tapers from a proximal end to adistal end.
 13. A suture anchor, comprising: an elongate shank defininga longitudinal axis and having at least one bone-engaging thread formedthereon; and a drive head having a proximal end and a distal end matedto the elongate shank, the drive head having an oval shapedcross-section, at least one suture attachment member, and at least onelongitudinally oriented suture receiving channel formed in a portion ofthe drive head, wherein the suture attachment member comprises first andsecond suture tunnels extending transversely through the drive head, andwherein the first and second suture tunnels extend substantiallyperpendicular to each other.
 14. The suture anchor of claim 13, whereinthe first and second suture tunnels are formed proximal to the distalend of the drive head to form a channel-free portion in the drive head.